old staircase

Hi Experts, I have recently purchased a semi-detached 1930s house. As a part of the internal renovation, I want to change the turning of the staircase by making it straight from bend at bottom part. The problem is that currently staircase at 1/2 steps might not have 2m headroom at the bend...

Our house is almost 200 years old and the stairs is the original with a lot of repairs. As you can see in the picture there are massive gaps between the wall and the stairs. How do I fix this?